Used in the related art is resistance welding devices that weld conductors such as a metal plate by using, for example, a projection welding or a spot welding.
These welding devices carry out the joining by applying a current between objects to be joined for welding, concentrating the current at a joining area of the objects to be joined, and increasing a temperature of the joining area above a joinable temperature with Joule heat generated by the concentration of the current in that manner.
In such a welding device, the objects to be joined are good conductors such as metals from necessity to apply a current for the joining, and a shape such as a projection is provided at the joining area of the objects to be joined in order to concentrate the current.
For example, in Patent Document 1 (Japanese Published Unexamined Patent Application No. H5-283139 A), a resistance welding method of dissimilar metal terminals is disclosed.
A method in Patent Document 1 is described as a resistance welding method of dissimilar metal terminals for reliably welding normal flat plate-type dissimilar metal terminals, and carries out the joining by forming a projection for projection welding on a low-melting-point metal terminal small in heat capacity and radiating heat of the projection during the welding toward a high-melting-point metal plate large in heat capacity. More specifically, when a large current is applied instantaneously by using a capacitor-type direct current resistance welder, heat is lost (radiated) toward the high-melting-point metal plate large in heat capacity, which prevents an excess heat generation of the projection on the low-melting-point metal terminal small in heat capacity for the welding.
Another example of welding using a projection for projection welding is disclosed in Patent Document 2 (Japanese Published Unexamined Patent Application No. 2010-510641 W).
This aims for an effect to solve problems caused in a welding process, to improve productivity, and to reduce possibilities of defects by replacing low price competitive nickel, in a method for connecting to batteries by changing a plurality of battery connecting members from an expensive nickel plate member to a copper alloy plate member and further applying a corrosion prevention coating layer in order to prevent copper from oxidizing in air. More specifically, the copper does not generate a sufficient heat during the resistance welding due to high conductivity. Therefore, it is of great difficulty to carry out a welding process for connecting the copper to an electrode terminal, but formation of an embossed structure at one end of a connecting member causes a supplied current to concentrate at a projecting portion with the embossed structure. As a result, a resistance value increases on the projecting portion, from which heat is intensively generated. This leads a temperature of the projecting portion to a melting temperature. Thus, at this time, the welding is carried out by applying a physical pressure to the connecting member. The temperature of the projecting portion reaches the melting temperature faster than a temperature of a dent facing the projecting portion, which prevents the connecting member from adhering to a welding rod.
A technique relating to a printed wiring board is disclosed in Patent Document 3 (Japanese Published Unexamined Patent Application No. H6-36852 A). The technique disclosed in Patent Document 3 is described as a method for connecting a terminal to a printed wiring board, wherein a projecting part is joined to a conductor circuit with metal diffusion by providing a projecting part on a connecting surface of a tip part of the terminal and applying an ultrasonic vibration while fitting closely and pressurizing the projecting part of the terminal on a surface of the conductor circuit on a printed wiring board. In terms of the effects, it is described that the welding pressure and the ultrasonic vibration can be intensively and efficiently applied to the projecting part in joining to the conductor circuit with the metal diffusion.